A pressure sensor of such generic type for registering pressure of a medium relative to the surrounding atmospheric pressure includes: a pressure measuring cell having a measuring membrane and a platform, wherein pressure of the medium can act on a side of the measuring membrane facing away from the platform, and wherein the platform has a reference air opening, through which surrounding atmospheric pressure can act on a side of the measuring membrane facing the platform; and a support body, through which a reference air duct extends between a first surface section and a second surface section of the support body; wherein the pressure measuring cell is affixed to the support body with a pressure resistant, bonded adhesive; the reference air opening communicates with the reference air duct, in order to form a reference air path to the measuring membrane; and the bonded adhesive surrounds the reference air path.
The bonded adhesive is pressure bearing, i.e. it must essentially absorb without plastic deformation the force due to the difference between the pressure of the medium and the atmospheric pressure acting on the pressure measuring cell.
For pressure bearing connections in the field of construction and joining technology of pressure sensors, adhesives are required, which are distinguished by freedom from creep and high final strength. Suitable adhesives include, for example, epoxide adhesives.
A change of mechanical properties of the bonded adhesive can lead to changed mechanical stresses on the platform, and these stresses can then be transmitted through the platform to the measuring membrane.
Insofar as the reference air naturally has variable water content, it proves to be a problem that the named adhesives and their interfaces to other materials have high moisture sensitivity. A moisture loading of the bonded adhesive with the associated changes of the adhesive properties can, thus, result in a corruption of measured pressure values.
Hydrophobic, moisture impermeable adhesives or caulks, such as e.g. silicone rubber are, however, due to their low strength or due to their plasticity, not suitable, in the case of high pressure loadings, for obtaining dimensionally stable, pressure-bearing, sealed adhesion of a pressure measuring cell to a support body.